Simultaneous telemetric monitoring of the circadian changes in core and BAT temperature in rats: Endogenous vasopressin may contribute to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle

The purpose of the present study was to analyze simultaneously the temporal relationship between the changes of circadian rhythms of brown adipose tissue (BAT) thermogenesis and core temperature (T-c) by dual probe telemetric monitoring transmitters and to determine the role of endogenous arginine vasopressin (AVP) in the circadian rhythms of BAT temperature (T-BAT) and T-c in male rats. The key observations in this study are: (1) Increase in T-BAT commenced approximately 8 min before T-c increases at the start of transition from the light to dark phase. Whereas at the start of transition from the dark to light phase, decrease in T-BAT commenced approximately 3 min before T-c decreases. The data show that circadian changes of BAT thermogenesis do indeed play a significant role in the overall maintenance of the circadian rhythm of core temperature. (2) The plasma AVP level was significantly elevated when core temperature decreases during the light phase, suggesting that endogenous AVP is involved in thermoregulatory processes during the light phase. V1a receptor antagonist could elevate core and BAT temperature during the light period, suggesting that endogenous AVP, acting through V1a receptor, could be involved in tonic thermoregulatory processes. V1a receptor antagonist can increase the blood lipid metabolism, suggesting that the mechanism of endogenous AVP in tonic thermoregulatory processes during light period could involve the suppression of lipolysis in BAT and other peripheral tissues. In summary, this study demonstrated that endogenous vasopressin contributes to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle. (C) 2011 Elsevier Ltd. All rights reserved.